Understanding Points
Reactivity 3.3.1—A radical is a molecular entity that has an unpaired electron. Radicals are highly reactive.
Reactivity 3.3.2—Radicals are produced by homolytic fission, e.g. of halogens, in the presence of
ultraviolet (UV) light or heat.
Reactivity 3.3.3—Radicals take part in substitution reactions with alkanes, producing a mixture of
products.
Radical: a chemical entity with an unpaired electron
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e.g. Cl⦁, ⦁CH3, ⦁OH
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Due to their high reactivity, radicals are usually formed as intermediates in a reaction
Bond breakage
Substitution reactions of alkanes
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Alkanes undergo substitution with halogens in UV light
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e.g. CH4 + 4Cl → CCl4 + 4HCl
1.
Initiation: radicals produced by homolytic cleavage of bond
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1.
Propagation: new radicals produced
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CH4 + Cl⦁ → ⦁CH3 + Cl⦁
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⦁CH3 + Cl2 → CH3Cl + Cl⦁
1.
Termination: radicals react together to form a non-radical product
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⦁Cl + ⦁Cl → Cl2
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⦁CH3 + ⦁Cl → CH3Cl
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⦁CH3 + ⦁CH3 → C2H6